1. Technical Field
Embodiments disclosed herein relate generally to systems and methods for producing polycrystalline diamond composites and cutting structures that have high thermal stability. More particularly, embodiments disclosed herein relate to a pressure vessel system capable of removing binder or catalyst material from polycrystalline diamond cutting structures that are attached to a substrate.
2. Background Art
Polycrystalline diamond compact (PDC) cutters have been used in industrial applications including rock drilling and metal machining for many years. In a typical application, a compact of polycrystalline diamond (PCD) (or other superhard material) is bonded to a substrate material, which is typically a sintered metal-carbide to form a cutting structure. PCD comprises a polycrystalline mass of diamonds (typically synthetic) that are bonded together to form an integral, tough, high-strength mass or lattice. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.
PCD may be formed by subjecting a volume of diamond grains to certain high-pressure/high-temperature (HPHT) conditions in the presence of a sintering aid or binder. Conventionally, the sintering aid or binder is provided in the form of a solvent metal catalyst material, such as one or more element from Group VIII of the Periodic table. The solvent metal catalyst may be added and mixed with the diamond grains prior to HPHT processing and/or may be provided during the HPHT process by infiltration from a substrate comprising the solvent metal catalyst as one of its constituent materials.
A conventional PDC cutter may be formed by placing a cemented carbide substrate into the container of a press. A mixture of diamond grains or diamond grains and catalyst binder is placed atop the substrate and treated under high pressure, high temperature conditions. In doing so, metal binder (often cobalt) migrates from the substrate and infiltrates into the diamond grain volume to promote intercrystalline bonding therebetween, thereby forming a sintered diamond body that is bonded to the substrate. The substrate often comprises a metal-carbide composite material, such as tungsten carbide. The deposited diamond body may be provided in the form of and referred to as a “diamond layer,” a “diamond table,” or an “abrasive layer.” The solvent metal catalyst material in such conventional PCD is disposed within interstitial regions that exist between bonded-together diamond crystals.
An example of a drag bit for earth formation drilling having PDC conventional cutters is shown in FIG. 1. In FIG. 1, a drill bit 10 has a bit body 12. The lower face of the bit body 12 is formed with a plurality of blades 14, which extend generally outwardly away from a central longitudinal axis of rotation 16 of the drill bit. A plurality of cutters 18 are disposed side by side along the length of each blade. The number of cutters 18 carried by each blade may vary. The cutters 18 are individually brazed to a stud-like carrier (or substrate), which may be formed from tungsten carbide, and are received and secured within sockets in the respective blade.
Conventional PCD includes 85 to 95 percent by volume diamond and a balance of the binder or catalyst material, which is present in PCD within the interstices existing between the bonded diamond grains. Binder materials that are typically used in forming PCD include Group VIII elements, with cobalt (Co) being the most common binder material used.
As noted above, PDCs are useful for forming cutting elements, for example, PDC cutters, used in applications calling for high degrees of wear and abrasion resistance, such as drilling subterranean formations. A significant factor in determining the longevity of PDC cutters is the generation of heat at the cutter contact point, specifically at the exposed part of the PCD layer caused by friction between the PCD and the work material being engaged. This heat causes thermal damage to the PCD in the form of cracks (due to differences in thermal expansion coefficients), which lead to spalling of the PCD body or layer, and/or delamination between the PCD body and substrate, and/or back conversion of the diamond to graphite in the PCD body causing rapid abrasive wear. As a result, the thermal operating range of conventional PDC cutters is typically less than about 750° C.
Conventional PCD is stable at temperatures of up to about 700 to 750° C., after which observed increases in temperature may result in permanent damage to and structural failure of PCD. This deterioration in PCD is due to the significant difference in the coefficient of thermal expansion of the binder or catalyst material, for example, as compared to diamond. Upon heating of PCD during use, the catalyst material and the diamond lattice expands at different rates, which may cause cracks to form in the diamond lattice structure and result in deterioration of the PCD. Damage is also due to the catalyzed formation of graphite at diamond-diamond necks at high temperatures, leading to loss of microstructural integrity and strength loss.
Attempts to address these issues have involved removing the catalyst or binder material from the diamond body after the PCD has been formed. Strong acid solutions have been used in some instances to remove or “leach” the catalyst or binder material from the diamond lattice structure. This approach has been practiced on the entire diamond body, where the catalyst material has been removed from the entire diamond body, or has been practiced on only part of or a region of the diamond body. Examples of “leaching” processes may be found, for example, in U.S. Pat. Nos. 4,288,248 and 4,104,344. In these instances, an acid solution, typically nitric acid or combinations of several strong acids (such as nitric and hydrofluoric acid) may be used to treat the diamond table, removing at least a portion of the catalyst or binder material from the PCD. By leaching out the catalyst material from the entire diamond body, thermally stable polycrystalline (TSP) diamond may be formed. In certain embodiments, only a select portion or region of a diamond composite is leached, in order to gain thermal stability without losing impact resistance. As used herein, the term TSP includes both of the above (i.e., partially and completely leached) compounds. Interstitial volumes remaining after leaching may be reduced by either furthering consolidation or by filling the volume with a secondary material, such by processes known in the art and described in U.S. Pat. No. 5,127,923, which is herein incorporated by reference in its entirety.
While conventional leaching processes with nitric/hydrofluoric acid mixtures are somewhat successful in removing the catalyst or binder material from the PCD, they tend to be time consuming, for example, using mixtures of acids may easily take many weeks in order to leach out the catalyst or binder material. Additionally, conventional leaching processes are typically performed prior to the PCD being attached to a substrate, as the acids used in the processes cause significant damage (e.g., erosion) to the substrate. Further, the use and handling of acid solutions such as hydrofluoric acid presents potential safety, health, and environmental dangers. Still further, the use of such conventional leaching techniques presents certain limitations in the degree of catalyst and binder material, as well as other unwanted non-diamond materials, which may be removed from the PCD.
Accordingly, there exists a need for methods and apparatuses that may enhance the process of removing unwanted catalyst or binder materials from the PCD after the PCD is attached to a substrate. There also exists a need for methods and apparatuses that may accelerate the leaching process, and/or reduce the hazards inherent in the leaching process.